Control moment gyroscopes (CMGs) are commonly employed in satellite attitude control systems. A generalized CMG comprises an inner gimbal assembly (IGA) supported by a stator housing (e.g., basering structure). The IGA includes a rotor assembly comprised of an inertial element (e.g., a ring or cylinder) coupled to a shaft. A spin bearing is disposed at each end of the shaft to permit the rotor to rotate about a spin axis. A spin motor couples to and drives the rotor thus allowing momentum to be stored. A torque module assembly (TMA) is mounted to a first end portion of the stator housing, and a signal module assembly (SMA) is mounted to the second end portion of the stator housing opposite the TMA. The TMA functions to selectively rotate the IGA assembly about a gimbal axis orthogonal to the rotor spin axis, which results in the production of an output torque orthogonal to the rotor spin axis and proportional to the gimbal rate. The SMA functions to deliver electrical signals and power across the rotary interface to the electrical components of the IGA assembly (e.g., the spin motor and electronics). The TMA may further include one or more rotation sensors (e.g., a tachometer, a resolver, etc.) suitable for monitoring the rotational rate, commutation, and/or the angular position of the inner gimbal assembly. Finally, to permit the CMG to be mounted to a host spacecraft (e.g., a satellite), a spacecraft interface (e.g., an annular structure including a plurality of bolt apertures) is provided on the outer surface of the stator housing.
Weight and volume are amongst the primary concerns in CMG design. Conventional CMGs are generally able to achieve rotor speeds of 6,000 revolutions per minute (RPM) or more depending upon the particular characteristics of the rotor. Rotors capable of rotating at higher speeds (e.g., up to 40,000 RPM) have been developed. Such an increase in CMG rotor speed permits the size of the rotor, and thus the size and weight of the CMG and host spacecraft, to be decreased without a reduction in CMG output torque. However, high speed rotors do not enable the dimensions of the TMA or the SMA to be reduced. Thus, as the CMG decreases in size, rotor size becomes less important in determining CMG weight and volume while the dimensions of the TMA and SMA become more significant drivers. Consequently, the TMA and, to a lesser extent, the SMA may add undesirable weight and volume to CMGs employing high speed rotors as well as smaller CMGs with lower torque requirements.
To impart a desired torque to the host spacecraft, the TMA rotates the IGA, and thus the spinning rotor, about the gimbal axis. The spinning rotor contains stored momentum due to its inertia about the spin axis and rotational rate. The output torque, which is proportional to the gimbal rate applied by the TMA, acts about an axis that is orthogonal to the spin and gimbal axes. This torque is transmitted from the CMG rotor to the spacecraft through the IGA and the stator housing. This load path tends to be relatively flexible. As a result, conventional CMGs often provide a less than optimum rotor-to-spacecraft load path resulting in low bandwidth performance regarding the transmission of torque to the spacecraft. In addition, the heat conduction path from the rotor spin bearings to the spacecraft mounting interface may be relatively lengthy and inefficient.
Considering the above, it would be desirable to provide a CMG, especially a CMG employing a high speed rotor, that is readily scalable, that has a high stiffness rotor-to-spacecraft load path, and that has a relatively efficient thermal conduction path. Preferably, such a CMG would employ a momentum control system that eliminates the need for a discrete TMA sub-assembly and thereby reduces the overall weight, volume, and part count of the CMG. Other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.